Two algorithms have been used in a hybrid scheme in order to obtain sea iceconcentration maps at 12 km resolution from 19, 37, and 85 GHz SSM/I data.The first one is an algorithm based on the polarization difference near 90GHz and the second one is the NASA Team algorithm which uses the 19 and 37GHz SSM/I channels. Ice concentrations are calculated using the 85 GHzchannels. In addition, the lower frequency channels are used to decidewhether the data points belong to the ice-free ocean or to the ice-coveredarea. This combination of high and low frequency channels eliminatesincorrect high ice concentrations caused by weather effects over the in factice-free ocean using the rather weather independent low frequencies whileretaining high resolution over ice with the high frequency. The estimationof proper tie points for the 85 GHz algorithm was a major task. Astatistical linear regression method for reference brightness temperatureestimation was applied in order to avoid misarranged guesses of the tiepoints. This method requires independent ice concentration reference datawhich were derived from aircraft dual-polarized passive microwavemeasurements at 19 and 37 GHz and optical line scanner images. ERS-2 SARimages were used to analyze the capability of the SSM/I to resolve featuressuch as the evolution of the marginal ice zone in the Fram Strait and theStorfjorden Polynya. Two different numerical atmospheric models were used toanalyze the effect of an increased resolution of ice data from 50 to 12 kmon the model results. It was found that the representation of the ice edgezone significantly influences the modelled atmospheric boundary-layertemperatures. The temperatures obtained with the high resolution ice dataagree significantly better with aircraft observed data.